Hello @kozmonauta,
I understand your goal a little better. You can use placeholders in the Advanced Form block when you set an email address by using the field name enclosed in brackets: {field-name}
Here is an example that should accomplish your goal. First, add a select field for the user to select options A, B, or C. The Select field has settings to add option labels and values. For the first option’s value, add the first email address. The second option’s value should be the second email address. The same is true for the third option value and the third email address. Give the Select field a field name something like email-to.
Then, add {email-to} as the email to address in the form setting and save the form. When the user selects A, B, or C, the value of the Select field will update to the selected email address, and the placeholder will dynamically adjust the address that receives the email.
Please let me know if you have more questions about this or if it works for you.